SNDCP, Sub Network Dependent Convergence Protocol, is part of

layer 3 In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transf ...

of a

GPRS General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Inst ...

protocol specification. SNDCP interfaces to the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

at the top, and to the GPRS-specific

Logical Link Control In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer acts as an interface ...

(LLC) protocol at the bottom. In the spirit of the GPRS specifications, there can be many implementations of SNDCP, supporting protocols such as

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts a ...

. However, in reality, IP (Internet Protocol) is such an overwhelming standard that X.25 has become irrelevant for modern applications, so all implementations of SNDCP for

only support IP as the payload type. The SNDCP layer is relevant to the protocol stack of the mobile station and that of the

SGSN The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile telephony, mobile networks to transmit Internet Protocol, IP packets to external networks such as the Internet. The GPRS syst ...

, and works when a

PDP Context The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile telephony, mobile networks to transmit Internet Protocol, IP packets to external networks such as the Internet. The GPRS syst ...

is established and the

quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

has been negotiated.

Services offered by SNDCP

The SNDCP layer primarily converts, encapsulates and segments external network formats (like

Datagrams) into sub-network formats (called SNPDUs). It also performs compression of NPDUs to make for efficient Data transmission. It performs the multiple

PDU transfers and it also ensures that NPDUs from each

are transmitted to the LLC layer in sufficient time to maintain the QoS. SNDCP provides services to the higher layers which may include connectionless and connection-oriented mode, compression, multiplexing and segmentation.

References

3GPP TS 44.065
''"Mobile Station (MS) - Serving GPRS Support Node (SGSN); Subnetwork Dependent Convergence Protocol (SNDCP)"'' Network protocols {{Wireless-stub