ANSI C12.22, IEEE 1703 and MC12.22 Transport Over IP

The ANSI C12.22 standard provides a set of application layer messaging services that are applicable for the enterprise and End Device components of an Advanced Metering Infrastructure (AMI) for the Smart Grid. The messaging services are tailored for, but not limited to, the exchange of the data Tables Elements defined and co- published in ANSI C12.19 , IEEE P1377 , and MC12.19 . These standards were developed jointly by ANSI (ANSI C12.22 and ANSI C12.19), by IEEE (IEEE 1377 and IEEE 1703) and Measurement Canada (MC12.19 and MC12.22). ANSI C12.22, which is an application-level messaging protocol, may be transported over any underlying transport network. This RFC defines the requirements governing the transmission of ANSI C12.22 Messages via the TCP and UDP transports in IP networks (whereby the OSI Session, Presentation, and Application Layers of ANSI C12.22 are collapsed into a single Application Layer). Specifically, this RFC applies to the operational details of Section 5, C12.22 Node to C12.22 Network Segment Details, of ANSI C12.22, and covers the mapping, encoding, and interpreting of ANSI C12.19 Device Network Table Elements and Native Addresses for use on IP networks.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 . Throughout this document we use terms like ANSI C12.22 or ANSI C12.19, as in C12.22 Relay or ANSI C12.19 Device. These terms are interchangeable with the terms IEEE 1703 Relay and IEEE 1377 Device, respectively. However, the recent versions of the Utility End Device communication standards were developed under the auspices of ANSI C12 SC17 WG1 and ANSI C12 SC17 WG2. For that reason, the terminology used in this document expands on the ANSI C12.22-2008 and ANSI C12.19-2008 definitions as revised by IEEE 1703-2009 and IEEE 1377-2010 .

This specification uses a number of terms to refer to the roles played by participants (actors) in, and objects of, the ANSI C12.22 , IEEE 1703 , and MC12.22 protocol. Terms prefixed by C12.22 or C12.19, which are not defined here, can be resolved in , , or , , . Association Control Service Element. In the context of this specification and of , ACSEs are encoded per ISO/IEC 10035-1 using the ASN.1 BER . Active-OPEN UDP is a state used by a local C12.22 IP Node to expect and receive incoming C12.22 Messages that it solicited from a foreign C12.22 IP Node using the UDP. The local C12.22 IP Node MAY exit the Active-OPEN UDP state when it has received all of the expected C12.22 Messages or a C12.22 Message timeout has occurred. The local C12.22 IP Node receives all C12.22 Response Messages solicited from the foreign C12.22 IP Node that arrive at the local port number that matches the source port number used to solicit the C12.22 Messages from the foreign C12.22 IP Node. Active-OPEN TCP is a state used by a local C12.22 IP Node to establish a TCP connection with a fully-specified foreign C12.22 IP Node using TCP and the foreign C12.22 IP Node's registered Native IP Address. The Active-OPEN TCP state is identical to "local active OPEN" defined in . Application Protocol Data Unit. In the context of the ANSI C12.22 Application, it is an ACSE C12.22 Message. ACSE Application Protocol Data Unit; same as APDU. An ANSI C12.22 Application-process Title. An ApTitle is a name for a system-independent application activity that exposes application services to the application agent; e.g., a set of application service elements that together perform all or part of the communication aspects of an application process. An ApTitle is encoded as a unique registered (as per ) object identifier. A C12.22 Node that is located on a C12.22 IP Network Segment and communicates using the IP protocol. A collection of all C12.22 IP Nodes that implement the IP-based protocols, as defined in this specification, and can communicate with each other using IP routers, switches, and bridges and without the use of a C12.22 Relay. A C12.22 IP Node that performs the functions of a C12.22 Relay. A C12.22 IP Relay acts as a bridge between a C12.22 IP Network Segment and an adjacent, C12.22 Network Segment. An ACSE APDU that is also a fully assembled or a segment of a C12.22 Request Message or a C12.22 Response Message. The C12.22 Message described in this specification MUST be encoded using . A fully assembled C12.22 APDU that contains an ACSE user-information element, which includes one or more EPSEM service requests. A fully assembled C12.22 APDU that contains an ACSE user-information element, which includes one or more EPSEM service responses. A logical and physical binding between two or more users of a service . Extended Protocol Specification for Electronic Metering. EPSEM defines structures and services used to encode multiple requests and responses for use by devices such as gas, water, electricity, and related electronic modules or appliances. A role of a C12.22 IP Node in which it initiates the transmission of a C12.22 Request Message. The term Native Address refers to the transport address that may be used to reach a C12.22 Node on its C12.22 Network Segment . In this specification the Native Address refers to the Native IP Address. Passive-OPEN UDP is a state used by a local C12.22 IP Node to expect and receive incoming C12.22 Messages from any foreign C12.22 IP Node using the UDP. When the Passive-OPEN UDP state is active, the local C12.22 IP Node accepts all C12.22 Messages that arrive at the local port number that was registered by the local C12.22 IP Node. Passive-OPEN TCP is a state used by a local C12.22 IP Node that wants to establish a TCP connection with an unspecified foreign C12.22 IP Node using TCP. In this case any foreign C12.22 IP Node MAY connect to the local C12.22 IP Node as long as the local port matches the port used by the foreign C12.22 IP Node. The Passive-OPEN TCP state is identical to "local passive OPEN" defined in . A role of a C12.22 IP Node in which it responds to the reception of a C12.22 Request Message. The C12.22 IP Node that is the destination for a C12.22 Message.

This section defines the characteristics of the C12.22 IP Network Segment.

A C12.22 Network Segment is a collection of C12.22 Nodes that can communicate with each other directly - without having to forward C12.22 Messages through a C12.22 Relay. A C12.22 IP Network Segment comprises C12.22 IP Nodes and the network infrastructure that enables any one node to reach all other nodes on the same segment. All C12.22 IP Nodes on the C12.22 IP Network Segment employ the same IP address encoding scheme (per Figures and ) and the same network and transport protocols in accordance with this specification. There is no restriction on the size of a C12.22 IP Network Segment. It MAY be as small as a single LAN or subnet, or it MAY include numerous, heterogeneous LANs and WANs connected by routers, bridges, and switches. The C12.22 IP Network Segment MAY be completely private, or include communication across the global Internet.

The term Native IP Address denotes a Native Address that MAY be used to reach a C12.22 Node on its C12.22 IP Network Segment. The Native IP Address includes the binary IP address, and an OPTIONAL port number that MAY be followed by an OPTIONAL protocol identifier. The Native IP Address SHALL be encoded as described in Section , . The IP address of the C12.22 IP Node MUST be configured before the C12.22 IP Node attempts to send or receive any C12.22 Message on its C12.22 IP Network Segment. If the port number is not explicitly configured by the controlling application, it SHALL be set to the default port number, 1153 (see Section , ). It is beyond the scope of this specification to define the method of configuration, the configuration parameters, or any administrative controls that the system administrator may wish to implement to assign an IP address.

ANSI C12.22 defines binary fields for encoding a C12.22 Native Address for transport within C12.22 Messages and for storage in C12.19 Device Tables. In this RFC the fields SHALL contain an IPv4 or an IPv6 binary native IP network address that is followed by an OPTIONAL two-byte TCP or UDP port number. The TCP or UDP port number, when present, MAY be followed by an OPTIONAL one-byte transport protocol identifier ("Protocol" of IPv4 or "Next Header" of IPv6). The transport protocol identifier SHALL be set to 17 (0x11) for UDP transport, or to 6 (0x06) for TCP transport, or not set (absent) for both UDP+TCP transports. The transport protocol values SHALL be consistent with the C12.22 Node's registered attributes (see CL and CO flags in Section , ). ANSI C12.22 allows the Native Address fields to be conveyed in select ANSI C12.22 EPSEM service elements (e.g., ANSI C12.22 Registration Service <native-address> parameter, ANSI C12.22 Resolve Service response <local-address>, and ANSI C12.19 INTERFACE_CTRL_TBL Element NATIVE_ADDRESS). The length of the C12.22 Native Address is qualified by an ANSI C12.22 address length field (e.g., ANSI C12.22 Registration Service <address-length> parameter, ANSI C12.22 Resolve Service response <local-address-length>, and ANSI C12.19 ACT_NETWORK_TBL Element NATIVE_ADDRESS_LEN). The ANSI C12.22 Registration Service permits only one Native Address to be recorded with each registered ApTitle. For this reason, a C12.22 IP Node that wishes to register different port numbers for UDP and TCP MUST register twice using different ApTitles. The binary Native IP Address fields SHALL be encoded in network byte order as shown in Figure .

Address IP Address (ADDR), Port (P), Transport (T) Length Octet 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 4 | ADDR4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4+Port 6 | ADDR4 | P | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4+Port 7 | ADDR4 | P |T| +Transport +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6 16 | ADDR6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6+Port 18 | ADDR6 | P | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6+Port 19 | ADDR6 | P |T| +Transport +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ When an ANSI C12.22 Native Address is encoded in ANSI C12.19 Tables' BINARY data Elements then the size of the native address Element is defined by ACT_NETWORK_TBL.NATIVE_ADDRESS_LEN (See and Table 121). This is the actual number of octets that are placed inside the C12.19 BINARY Element. This value is common to all of the C12.22 Node's interfaces, including those that are not IP based (thus not conforming to this specification). For this reason the ACT_NETWORK_TBL.NATIVE_ADDRESS_LEN MAY be greater than, and SHALL NOT be smaller than, the actual length needed to encode a Native IP Address per Figure . When this is the case, the C12.22 Native IP Address SHALL be padded with zero (0) to fill the Table's BINARY data Element. In instances where the Native IP Address length does not exactly match any of the Address Lengths listed in Figure , the actual Address Length SHALL be determined by stripping all trailing binary zeros (0x00) and then adjusting the Address Length upwards to the next largest value shown in Figure .

IANA (Internet Assigned Numbers Authority) has assigned port 1153 for UDP and TCP C12.22 IP Messages. By default, C12.22 IP Nodes SHALL send all C12.22 Application Association initiation message requests set with 1153 as the destination port number. To ensure interoperability among C12.22 IP Nodes, all C12.22 IP Relays and Master Relays SHALL monitor and accept UDP and TCP messages destined to port 1153. Any IP firewalls or Access Control Lists (ACLs) shielding C12.22 Nodes and the IP network MUST be configured to forward UDP and TCP traffic destined to port 1153 and other ports that are assigned and registered by the Network administrator, in order to maintain the continuity of the C12.22 IP Network Segment.

Although RFC 768 allows for a source port number of zero (0), C12.22 IP Nodes SHALL NOT send datagrams on UDP with the source port set to zero. A C12.22 IP Node SHALL ignore and SHALL NOT respond to any C12.22 Message that it receives from source port 0. Further details of C12.22 IP Node's use of UDP, and of TCP, are given in Section , .

In addition to unicast, the ANSI C12.22 protocol requires the support of a multicast message delivery service from the network. In cases where C12.22 IP Nodes MUST perform Native IP Address discovery (e.g., the discovery of the Native IP Address of C12.22 IP Relays that provide a route out of the C12.22 IP Network Segment, or the discovery of the Native IP Address of a C12.22 IP Master Relay on the C12.22 IP Network), the C12.22 IP Nodes use IP Multicast to send a C12.22 Message that contains an EPSEM Resolve Service Request on the IP LAN. IP multicast is also desirable, for example, when a C12.22 Host needs to read a multitude of C12.22 Nodes (e.g., meters) that are configured with a common C12.22 multicast group ApTitle. Using IP multicast, the C12.22 Host MAY send a C12.22 Message containing an EPSEM Read Service Request that reaches all C12.22 Nodes on the C12.22 IP Network Segment. For these reasons, all C12.22 IP Relays and Master Relays SHALL support IP multicast and it is RECOMMENDED that all C12.22 Nodes support IP multicast. Any IPv4 C12.22 IP Node that supports IP multicast SHALL use the Internet Group Management Protocol IGMP version 1 (IGMPv1) as a minimum, to report (i.e., request) membership in the C12.22 multicast group to its local router(s). It is RECOMMENDED that C12.22 IP Nodes implement IGMPv3 . Any IPv6 C12.22 IP Node that supports IP multicast SHALL use Multicast Listener Discovery version 2 (MLDv2) (RFC 3810 ) possibly within ICMPv6 (RFC 4443 ) to report membership. Routers that interconnect C12.22 IP Nodes on the C12.22 IP Network Segment MUST support Protocol Independent Multicast Sparse Mode (PIM SM) (RFC 4601 ) along with IGMPv1 (RFC 1112 ) as a minimum for IPv4, or MLDv2 for IPv6 (RFC 3810 ). It is RECOMMENDED that they implement IGMPv3 . It is beyond the scope of this specification to define the mechanism for selecting an initial Rendezvous Point (RP) for the C12.22 multicast group, the use of shared versus source trees, or the mechanism for inter-domain multicast routing. IANA has registered the "All C1222 Nodes" multicast group, and has assigned the IPv4 multicast address of 224.0.2.4 and the IPv6 multicast address of FF0X::204, where X represents the Scope field as defined in RFC 4291, the IP Version 6 Addressing Architecture . For IPv6, all C12.22 IP Relays, C12.22 IP Master Relays, and all C12.22 IP Nodes configured to support broadcast and multicast (see Section , ) SHALL join the global scope multicast address, FF0E::204, as well as all of the assigned, reduced-scope, multicast addresses:

link-local - FF02::204; admin-local - FF04::204; site-local - FF05::204; and organization-local - FF08::204. IPv6 C12.22 IP Nodes SHOULD use the minimum scope needed, when initiating IP multicast messages to reach another C12.22 IP Node on the C12.22 Network. This practice allows the sender to limit unnecessary propagation of C12.22 IP multicast Messages. To determine the minimum scope required to reach the closest C12.22 IP Relay on the C12.22 Node's IP Network Segment, this specification RECOMMENDS the following simple steps: Starting with the smallest (local-most) scope, link-local (or a pre-configured scope), send the C12.22 EPSEM Resolve Service Request for C12.22 IP Relay discovery. Listen for a response from a C12.22 IP Relay; then: If no response is received, assign the next wider scope level, then repeat steps (1) and (2) at the newly assigned scope. If a response is received then record the scope level as the minimum scope to use on the node's C12.22 IP Network Segment. A C12.22 IPv6 Node that initiates any EPSEM Service Request SHOULD use the minimum scope necessary to reach its target C12.22 IP Nodes. A C12.22 IPv6 Relay SHALL use the global scope for any C12.22 message destined for the global Internet. This specification does not preclude the use of the unassigned scope values defined in ; those scope values MAY be used on a private basis, or through mutual operating agreements. For IPv4, all C12.22 IP Relays, C12.22 IP Master Relays, and all C12.22 IP Nodes configured to support broadcast/multicast SHALL join the assigned multicast address of 224.0.2.4. This global address does not provide for the type of scoping discussed above for IPv6, nor is it compatible with the administratively scoped IP multicast specification in RFC 2365 . Therefore, a different technique to limit the propagation of C12.22 IP multicast Messages is needed. One available technique to control IPv4 multicast scope is through the use of the Time-to-Live (TTL) attribute in the IP packet header. This attribute is not managed by the C12.22 protocol. In the implementation of this technique, an administrative domain MUST include at least one C12.22 IP Relay, and all C12.22 IP Nodes in the administrative domain SHOULD be configured with a TTL sufficiently large to reach that C12.22 IP Relay. A C12.22 IPv4 Node that initiates any C12.22 Request Message SHOULD use the minimum TTL needed to reach its target C12.22 IP Nodes.

IP broadcast is not generally suitable as a replacement for, or an alternative to multicast in a C12.22 IP Network Segment. IP broadcast is not supported in IPv6 and it suffers from limited scope in IPv4. This specification, however, does not preclude the use of IP network directed or limited/local scope (address 255.255.255.255) broadcast within a controlled management domain (as per RFC 2644 ).

ANSI C12.22 Tables provide binary Elements for encoding a Native Broadcast or Multicast Address for transport within a C12.22 Message. The encoding of these Table Elements is identical to that defined in Section , . These fields SHALL be used as shown in Figure .

Address IP Address (ADDR), Port (P), Transport (T) Length Octet 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Broadcast 4 |BADDR4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Broadcast 6 |BADDR4 | P | +Port +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Broadcast 7 |BADDR4 | P |T| +Port+Transport +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 4 |MADDR4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 6 |MADDR4 | P | +Port +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 7 |MADDR4 | P |T| +Port+Transport +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 16 | MADDR6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 18 | MADDR6 | P | +Port +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv6 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Multicast 19 | MADDR6 | P |T| +Port+Transport +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The IPv4 and IPv6 multicast addresses, MADDR4 and MADDR6, respectively, are those assigned by IANA for use by ANSI C12.22. When a broadcast/multicast Native IP Address is encoded in ANSI C12.19 Tables' BINARY data Elements the size of the Native Address Element transmitted is defined by ACT_NETWORK_TBL.NATIVE_ADDRESS_LEN (See and Table 121). This is the actual number of octets that are placed inside the C12.19 BINARY Element. This value is common to all of the C12.22 Node's interfaces, including those that are not IP based (thus not conforming to this specification). For this reason the ACT_NETWORK_TBL.NATIVE_ADDRESS_LEN MAY be greater than, and SHALL NOT be smaller than, the actual length needed to encode a native IP broadcast/multicast address per Figure . When this is the case, the C12.22 Native IP Address SHALL be padded with zero (0) to fill the Table's BINARY data Element. The IPv4 network directed broadcast address can be computed by performing a bitwise OR between the bit complement of the subnet mask of the target IP subnet and the IP address of any host on that IP subnet.

This section defines a C12.22 Node's usage of the Connection-Oriented (CO) and Connectionless (CL) transport layer protocols, TCP and UDP, respectively.

A C12.22 IP Node's use of TCP and UDP is based on its registered capabilities as defined in its configuration parameters (flags) and as expressed in the Node's accepted registration attributes :

CL Flag = <connection-type>.CONNECTIONLESS_MODE_SUPPORTED; CL Accept Flag = <connection-type>.ACCEPT_CONNECTIONLESS; CO Flag = <connection-type>.CONNECTION_MODE_SUPPORTED; and CO Accept Flag = <connection-type>.ACCEPT_CONNECTIONS. The mapping of the connection-type parameters to the IP-based transport variants that a C12.22 Node MAY support is defined in Table . CL Flag CO Flag CL Accept Flag CO Accept Flag IP Transport Mode Supported 0 0 x x Invalid 0 1 0 0 TCP, Active-OPEN 0 1 0 1 TCP, Passive- and Active-OPEN 0 1 1 0 Invalid 0 1 1 1 Invalid 1 0 0 0 UDP, Active-OPEN 1 0 0 1 Invalid 1 0 1 0 UDP, Passive- and Active-OPEN 1 0 1 1 Invalid 1 1 0 0 UDP, Active-OPEN; TCP Active-OPEN 1 1 0 1 UDP, Active-OPEN; TCP, Passive- and Active-OPEN 1 1 1 0 UDP, Passive- and Active-OPEN; TCP, Active-OPEN 1 1 1 1 UDP, Passive- and Active-OPEN; TCP, Passive- and Active-OPEN Every C12.22 IP Node MUST support at least one of unicast CO or CL operating capabilities (as advertized in Decade 12, Network Tables , where available, and as registered using the C12.22 Registration Service ).

General rules: A C12.22 IP Node that implements [CL Accept=1] SHALL receive incoming UDP C12.22 Messages on its registered Native IP Address (IP address and port number). A C12.22 IP Node that implements [CO Accept=1] SHALL receive incoming TCP connections on its registered Native IP Address (IP address and port number). A C12.22 IP Relay that forwards a UDP C12.22 Message to a C12.22 IP Node on the C12.22 IP Network Segment SHALL send the C12.22 Message to the C12.22 IP Node's registered Native IP Address (IP address, port number). A C12.22 IP Relay that forwards a TCP C12.22 Message to a C12.22 IP Node on the C12.22 IP Network Segment MAY use an established TCP connection to that C12.22 IP Node, or it SHALL establish a new TCP connection to the C12.22 IP Node's registered Native IP Address (IP address and port number). A C12.22 IP Node that implements [CL=1] SHOULD set the source port number in outbound UDP C12.22 Messages to its registered port number. When the target UDP C12.22 IP Node is reachable using direct messaging (as defined in ), the C12.22 IP Node MAY set the source port number to a UDP port number that is different than its registered port number. When the registered Native IP Address of a C12.22 IP Node does not include the OPTIONAL port number, then port 1153 SHALL be assumed and used as the registered port number. All C12.22 IP Nodes SHOULD use port 1153 in their Native IP Address when registering.

A C12.22 IP Node that supports this mode SHALL NOT monitor for unsolicited incoming C12.22 Messages via UDP. As a result, the C12.22 IP Node is incapable of receiving unsolicited C12.22 Messages using UDP. The C12.22 IP Node MAY enter the Active-OPEN UDP state by initiating an unsolicited UDP transmission to a Target C12.22 IP Node, which is expected to implement the Passive-OPEN UDP mode. C12.22 IP Nodes SHOULD use their registered UDP port number, or if not yet registered then they SHOULD use port 1153, as the source port number for all UDP C12.22 IP Messages.

A C12.22 IP Node that operates in this mode SHALL be capable of receiving solicited and unsolicited C12.22 Messages from other C12.22 IP Nodes. The C12.22 Node MAY change the port number that it monitors by using the <native-address> parameter of the ANSI C12.22 Registration Service. The C12.22 IP Node MAY initiate unsolicited Active-OPEN UDP transmissions to other C12.22 IP Nodes that implement the Passive-OPEN UDP mode. When operating in this mode, the C12.22 IP Nodes SHALL use their registered UDP port number as the source port number for all UDP C12.22 IP Messages. All C12.22 IP Relays SHALL support the Passive-OPEN UDP mode. C12.22 Authentication Hosts and C12.22 Notification Hosts that implement UDP SHALL support Passive-OPEN UDP mode. For all other C12.22 IP Nodes, Passive-OPEN UDP mode is the RECOMMENDED mode when implementing UDP.

A C12.22 IP Node that supports this mode SHALL NOT monitor for inbound TCP connections. As a result, the node is incapable of accepting incoming connections via TCP. The C12.22 IP Node MAY initiate TCP connections to Target C12.22 IP Nodes, which are expected to implement the Passive-OPEN TCP mode. In this mode, C12.22 Messages exchanged by a pair of associated C12.22 IP Nodes can only be communicated through any of the TCP connections that were initiated by the C12.22 IP Node that implements this mode. The loss or closure of a connection SHALL NOT automatically result in the termination of the C12.22 associations between the peer nodes. In order to continue exchanging C12.22 Messages without loss of association, the initiating C12.22 IP Node MAY re-establish new TCP connections with the peer node, or use existing connections to the peer node. The termination of the C12.22 Application associations is dependent upon C12.22 application timeout attributes and C12.22 link management services (such as Procedure 25 Network Interface Control ).

A C12.22 IP Node that operates in this mode SHALL monitor and accept incoming TCP connections. The C12.22 Node May change the port number that it monitors by using the <native-address> parameter of the ANSI C12.22 Registration Service. The C12.22 IP Node MAY initiate Active- OPEN TCP connections to other C12.22 IP Nodes that implement the Passive-OPEN TCP mode. In this mode, C12.22 Messages exchanged by a pair of associated C12.22 IP Nodes can arrive through any of the TCP connections that were established by either node. The loss or closure of a connection SHALL NOT automatically result in the termination of the C12.22 associations between the peer nodes. In order to continue exchanging C12.22 Messages without loss of association, either C12.22 IP Node MAY re-establish new TCP connections with the peer node, or use existing connections to the peer node. The termination of the C12.22 Application associations is dependent upon C12.22 application timeout attributes and C12.22 link management services (such as Procedure 25 Network Interface Control ). All C12.22 IP Relays SHALL support the Passive-OPEN TCP mode. C12.22 Authentication Hosts and C12.22 Notification Hosts that implement TCP SHALL support Passive-OPEN TCP mode. For all other C12.22 IP Nodes, Passive-OPEN TCP mode is the RECOMMENDED mode when implementing TCP.

C12.22 IP Nodes MAY use TCP in one of two ways: bi-directional traffic flow or uni-directional traffic flow. When TCP connections are used, any new or established TCP connection between the two C12.22 IP Nodes MAY be used equivalently by the C12.22 IP Nodes to send and to receive C12.22 Messages. This is the RECOMMENDED and default mode of operation because ANSI C12.22 requires the transport network to be reliable and connectionless (per connectionless-mode ACSE). For this reason ANSI C12.22 defines peer- to-peer application associations and not peer-to-peer connections. It is known that some C12.22 implementations have been deployed in which TCP is used for uni-directional traffic flow. For these types of implementations, an established TCP connection SHALL be used by the initiator of that connection to send C12.22 Messages and by the target node (who accepted the connection) to receive C12.22 Messages. If a C12.22 IP Node wishes to send a C12.22 Message to a peer C12.22 IP Node, it MUST establish and use a new TCP connection or use an existing TCP connection that it had previously initiated, for its outbound uni-directional traffic flow. For increased interoperability, the initiator of the connection SHOULD accept incoming C12.22 Messages on that connection in case the target node attempts to use the connection for bi-directional traffic flow. Uni-directional use of TCP is a special mode of operation; it is NOT RECOMMENDED because multiple one-way channel communication is not described by ANSI C12.22, and it utilizes one-half of the TCP connection capability. As a result it doubles the number of TCP connections used to communicate C12.22 Messages, and thus could become a burden when a large number of connections is required.

A C12.22 IP Node's use of Broadcast/Multicast is based on its capabilities as defined in its configuration parameters (flags) and as expressed in the Node's accepted registration attributes (<connection-type>.BROADCAST_AND_MULTICAST_SUPPORTED). The mapping of the C12.22 IP Node's Broadcast/Multicast parameter (flag) to IP Broadcast/Multicast usage is defined in Table . C12.22 Broadcast and Multicast Supported Flag IP Broadcast/Multicast Supported 0 The C12.22 IP Node does not accept IP broadcast and it does not accept IP multicast messages. 1 The C12.22 IP Node accepts both IP broadcast (IPv4 only) and IP multicast messages (IPv4 and IPv6). If a C12.22 IP Node is configured to accept IP broadcast and multicast messages, it SHALL join the "All C1222 Nodes" multicast group (see Section , ), and SHALL use the default port 1153. In addition it SHALL accept IP Network directed or limited (local scope) broadcast messages sent to port 1153. Note that successful communication using network directed broadcast requires configuration of network routers, which by default SHALL NOT forward directed broadcasts as per RFC 2644 .

An initiating C12.22 IP Node MAY send any C12.22 Message using UDP or TCP. However, in accordance with Section 5.3.2.4.12, Resolve Service, of ANSI C12.22, it is RECOMMENDED that the C12.22 Resolve Request message be transported using UDP/IP multicast when the Native IP Address of the Target C12.22 Node is not known. Use of UDP/IP multicast is preferred over the use of IP network directed or limited broadcast; therefore when UDP/IP multicast is supported its use is RECOMMENDED over network broadcast.

When sending via UDP a large C12.22 Message that exceeds the path MTU, the sender SHALL segment the ACSE APDU in accordance with ANSI C12.22 Datagram Segmentation and Reassembly algorithm, such that the size of the resulting IP datagram does not exceed the path MTU, and thus avoids UDP packet fragmentation. The fundamental issue with fragmentation exists for both IPv4 and IPv6. Section 3.2 of RFC 5405 provides additional guidelines for determining the appropriate UDP message side. When path MTU is not known, the sender SHALL follow the guidelines stipulated in Section 3.2 of RFC 5405 : for IPv4 use the smaller of 576 bytes and the first-hop MTU , and for IPv6 use 1280 bytes . Sending large APDUs via UDP may lead to network congestion. For more information on avoiding network congestion see Section , .

When a Target C12.22 IP Node receives a C12.22 Request Message from an initiating C12.22 IP Node, it SHALL send a C12.22 Response Message using the same transport protocol (i.e., TCP to TCP, UDP to UDP). In the case of UDP, the target SHALL send the C12.22 Response Message to the source IP address and port number.

The ANSI C12.22 standard provides a configuration parameter in the APDU's <calling-AE-qualifier>.URGENT to mark a message as urgent. There are numerous IP-based technologies that enable enhanced levels of message delivery and quality of service. This specification does not define the technology to be used to send urgent messages over IP.

Designers of unicast applications that implement the upper-layers of C12.22 Messaging over UDP SHOULD follow the congestion control guidelines in Section 3.1 of RFC 5405 . For the transmission of C12.22 Messages that are greater than what the TCP initial window would be over a given Internet path, TCP SHOULD be used rather than UDP as the transport protocol. TCP's initial window depends on the MSS, which in turn depends on the path MTU, and is computed according to formula (1) in RFC 3390 . For unknown path MTUs, the minimum-sized MSS MUST be used and the C12.22 Application SHOULD assume the maximum C12.22 Message size to be 2048 bytes. By using TCP the C12.22 Application benefits from the built- in TCP congestion control mechanism. When UDP is the preferred transport mechanism or when UDP multicast or broadcast are the preferred modes of communication, then the C12.22 application SHOULD use C12.22 acknowledged Messages that are smaller than TCP's initial window over the return path, as computed by formula (1) in and described above. The size of the C12.22 Message MAY be managed through the use of ANSI C12.22 EPSEM Partial Table Read/Write service requests and responses.

The ANSI C12.22 Application layer security is defined in Section 5.3.4.13, C12.22 Security Mechanism, of the ANSI C12.22 standard. The security mechanisms include provisions for message privacy and authentication, playback rejection, and message acceptance windows as well as ANSI C12.19 role-based data access and secured register mechanisms. The ANSI C12.22 Application layer default security mechanism provides three options to choose from when sending C12.22 Messages: Sending clear text messages over the C12.22 Network , , which MAY result in altered C12.22 Messages and exposure to password sniffing attacks, as described in RFC 3552 . Sending of authenticated plain text messages over the C12.22 Network , , which MAY result in password sniffing attacks as described in RFC 3552 . Sending of authenticated cipher text over the C12.22 Network providing for message and peer node authentication and privacy. When option 1 is used then it is RECOMMENDED that the network or transport layer provide authentication and confidentiality service. When option 2 is used then it is RECOMMENDED that the network or transport layer provide confidentiality services. When option 3 is used then no additional network or transport layer security services are necessary. Additional Transport or Network layer security protocols are not required by ANSI C12.22, but they MAY be provided transparently by C12.22 IP Network Segment integrators (e.g., in C12.22 IP Relays) in order to improve on the security provisions cited above. However, any added Transport security (e.g., TLS, RFC 5246 ) or IP security (e.g., IPsec, RFC 4302 , RFC 4303 , RFC 5996 ) features SHALL act only to enhance (i.e., not be a substitute for, or an alteration of) the interoperable ANSI C12.22 and ANSI C12.19 security provisions, and SHALL NOT corrupt and SHALL NOT alter the C12.22 Message as presented by the C12.22 Application layer. The ANSI C12.22 and ANSI C12.19 standards provide for the transmission of keys and their storage in C12.19 End Devices (e.g., meters and Head-end systems). The key management protocol (when and how keys are exchanged) is not described in the ANSI C12.22 and ANSI C12.19 standards, except to state that keys MAY not be readable from a C12.19 End Device (in response to a read service request). It is RECOMMENDED that all C12.22 Nodes encrypt user information element key fields and passwords. It is also RECOMMENDED that all C12.22 Nodes mask user information element key fields and password fields of EPSEM Read Service Responses (e.g., by replacing all key and password bytes with zeros (0x00) or spaces (0x20)). Legacy deployments exist that are not connected to the Internet, so there are some implementations that do not include security. It is likely that multi-homed C12.22 Nodes with interfaces to the Internet will exist in future deployments, so security mechanisms MUST be used by those C12.22 Nodes to ensure C12.22 Message authentication and confidentiality.

UDP and TCP port 1153, which is used for C12.22 communication over IP, is registered with IANA. Section , defines the use of multicast. The following multicast addresses have been registered by IANA for use by the ANSI C12.22 standard: IPv4 - "All C1222 Nodes" address 224.0.2.4 IPv6 - "All C1222 Nodes" address FF0X::204

The authors wish to recognize Alexander Shulgin for providing valuable comments and for conducting feasibility testing in support of this work. The following people have improved this document through thoughtful comments and suggestions: Fred Baker, Ralph Droms, Vijay Gurbani, Michael Stuber, Spencer Dawkins, Alfred Hoenes, Russ Housley, Paul Hoffman, Lars Eggert and Sean Turner.