Editing My 3GPP TS 24.007 Notes (section)

=== 4.3.3 Protocols and peer-to-peer communication ===
By use of the services provided by lower (sub )layers, peer entities in a (sub )layer in the MS and the network exchange information. Exchange of information between two peer entities is performed according to the corresponding (sub )layer protocols. A protocol is a set of rules and formats by which the information (control information and user data) is exchanged between the two peers. The information is exchanged by use of messages which are defined in the protocol. (Therefore, the messages are also called Protocol Data Units, PDUs).

There are several protocols of the RR sublayer, one protocol of the LLC sublayer, three protocols of the MM sublayer, and several protocols of the CM sublayer. For each functional block of the CM sublayer as defined in clause 4.1 there is one protocol. The CM protocols are specified in the Technical Specifications identified in clause 4.3.4.

In the model used in the present document, there are:

...
<ol type="1" start="5">
<li>for EPS services:
* one RR entity in the MS and one RR entity in the network;
* one EMM entity in the MS and one EMM entity in the network;
* for each functional block of the CM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities.</li>
<li>for 5GS services:
* one 5GRR entity in the MS and one 5GRR entity in the network for NAS over 3GPP access;
* one non-3GPP access management entity in the MS and one non-3GPP access interworking entity in the N3IWF for the NAS over non-3GPP access;
* one 5GMM entity in the MS and one 5GMM entity in the network;
* for each functional block of the 5GCM sublayer as defined in clause 4.1 which is supported in the MS (in the network), there are, depending on the protocol, one or more entities in the MS (in the network). Two different entities of the same functional block in the MS (in the network) are called parallel entities. The entities of the same functional block in the MS correspond in a one-to-one relation to the entities of the functional block in the network. The corresponding entities are called peer entities.</li>
</ol>

As each sub layer entity is specified by one and only one protocol, it is also called a protocol entity or protocol control entity.

For GPRS-services supporting Class A and Class B MSs, the MM entities of the MM-sublayer are able to exchange information by means of GMM PDUs as well as MM PDU's. This means if a mobile is GPRS attached, non-GPRS mobility management procedures may make use of GRPS mobility management messages.

When two peer protocol entities exchange PDUs, a transaction is said to be established (or: to be active; or: to exist). It depends from the protocol when exactly a protocol entity considers the transaction to be active, normally this is the case:
* from the moment when it has passed the first suitable message to lower (sub-) layers or received the first suitable message from its peer entity;
* up to the moment when it has released the transaction.