The maximum bytes (Data + Variable name) per payload in a PCCE deployment is 2500 bytes. This is the limit imposed by the SIP protocol for the User to User Information (UUI) field that carries the ECC variables. Reference = [Cisco Unified Contact Center Enterprise Features Guide, Release 12.5(1)], page 23

The first step for CCE to dynamically allocate a label is an agent needs to log in, as this triggers the Agent PG to send a label request message to the Router. The Router then assigns a label from the available pool and sends it back to the Agent PG. Reference = [Cisco Unified Contact Center Enterprise Solution Reference Network Design (SRND), Release 12.5(1)], page 13

According to the Scripting and Media Routing Guide for Cisco Unified ICM/Contact Center Enterprise, Release 12.5 (1) and 12.5 (2), dynamic labels are expressions that the CallRouter processes in real time, converting an expression into a character string that is then returned to the routing client as a label1. Dynamic labels are useful for routing calls to agents based on their current location, availability, or skill level.For CCE to dynamically allocate a label, an agent needs to log in and register with the system, so that the CallRouter can access the agent's information and use it in the dynamic label expression1. The other options are not correct, because they are not related to dynamic label allocation.The WB ermine service is a web service that provides access to the configuration data of the system2.The Dialer is a component that enables outbound dialing campaigns3.The CVP Call service is a service that handles call control and voice processing for calls that use Unified CVP3.

1: Cisco Packaged Contact Center Enterprise Features Guide, Release 12.0 (1)

2: Cisco Packaged Contact Center Enterprise Administration and Configuration Guide, Release 12.0 (1)

3: Scripting and Media Routing Guide for Cisco Unified ICM/Contact Center Enterprise, Release 12.5 (1) and 12.5 (2) - Dynamic Labels

A distinction between Packaged CCE and Unified CCE, specifically regarding call transfers, is that transfers that require Service Provider interaction via the NIC are supported by a PCCE Deployment in a 2K deployment model only. This means that PCCE can only support pre-routing call flows with NIC in a limited scale, while UCCE can support pre-routing call flows with NIC in any deployment model. Reference = [Cisco Unified Contact Center Enterprise Solution Reference Network Design (SRND), Release 12.5(1)], page 101

The protocol used by CVP to communicate to VRU PG is GED-155, which stands for Generic External Device Protocol version 155. GED-155 allows CVP to send and receive messages from VRU PG for call control and data exchange. Reference = [Cisco Unified Contact Center Enterprise Solution Reference Network Design (SRND), Release 12.5(1)], page 11